Radial waveguide systems and methods for post-match control of microwaves

ABSTRACT

A system provides post-match control of microwaves in a radial waveguide. The system includes the radial waveguide, and a signal generator that provides first and second microwave signals that have a common frequency. The signal generator adjusts a phase offset between the first and second signals in response to a correction signal. The system also includes first and second electronics sets, each of which amplifies a respective one of the first and second microwave signals. The system transmits the amplified, first and second microwave signals into the radial waveguide, and matches an impedance of the amplified microwave signals to an impedance presented by the waveguide. The system also includes at least two monitoring antennas disposed within the waveguide. A signal controller receives analog signals from the monitoring antennas, determines the digital correction signal based at least on the analog signals, and transmits the correction signal to the signal generator.

TECHNICAL FIELD

The present disclosure is in the field of microwaves. More specifically,embodiments that utilize radial waveguides and associated controlsystems to provide control of microwaves in a plasma process chamber aredisclosed.

BACKGROUND

Semiconductor processing often generates plasmas to create ionizedand/or energetically excited species for interaction with semiconductorwafers themselves, or other processing related materials (e.g.,photoresist). To create and/or maintain a plasma, one or more radiofrequency (RF) and/or microwave generators are typically utilized togenerate oscillating electric and/or magnetic fields. The same fields,and/or DC fields, may also be utilized to direct the ionized and/orenergetically excited species to the semiconductor wafer(s) beingprocessed. Various known methods are often utilized to match animpedance of a power source (the RF generator) to a load (the plasma) sothat power from the RF generator is delivered to the plasma withoutsignificant reflection of power back to the RF generator. This is forreasons of energy efficiency as well as to protect electrical componentsof the RF generator from damage. Particularly when microwave energy isutilized, reflected power is usually directed to a dummy load where itis dissipated as heat, which must then be removed. Thus, reflected powerresults in a two-fold waste of energy: the energy utilized to generatethe power, and the energy utilized to remove the waste heat.

SUMMARY

In an embodiment, a system provides post-match control of microwaves ina radial waveguide. The system includes the radial waveguide and asignal generator that provides a first microwave signal and a secondmicrowave signal. The first and second microwave signals have a commonfrequency. The signal generator adjusts a phase offset between the firstand second microwave signals in response to a digital correction signal.The system also includes a first electronics set and a secondelectronics set. Each of the first and second electronics sets amplifiesa respective one of the first and second microwave signals to provide arespective first or second amplified microwave signal, transmits therespective first or second amplified microwave signal into the radialwaveguide, and matches an impedance of the respective first or secondamplified microwave signal to an impedance presented by the radialwaveguide. The system also includes at least two monitoring antennasdisposed within the radial waveguide. A signal controller receivesanalog signals from the at least two monitoring antennas, determines thedigital correction signal based at least on the analog signals from theat least two monitoring antennas, and transmits the digital correctionsignal to the signal generator.

In an embodiment, a system for plasma processing of a workpiece includesa process chamber configured to create a plasma for the plasmaprocessing, and a radial waveguide, adjacent to the process chamber,configured to generate microwaves for transmission to the processchamber to supply energy for the plasma. The system also includes asignal generator that provides a first microwave signal and a secondmicrowave signal, the first and second microwave signals having a commonfrequency. The signal generator adjusts a phase offset between the firstand second microwave signals in response to a digital correction signal.The system also includes a first electronics set and a secondelectronics set. Each of the first and second electronics sets amplifiesa respective one of the first and second microwave signals to provide anamplified microwave signal, transmits the amplified microwave signalinto the radial waveguide, and matches an impedance of the amplifiedmicrowave signal to an impedance presented by the radial waveguide. Thesystem also includes a signal controller that receives analog signalsfrom the at least two monitoring antennas, determines the digitalcorrection signal based at least on the analog signals from the at leasttwo monitoring antennas, and transmits the digital correction signal tothe signal generator. The first electronics set includes a tuner thatmatches the impedance of the first amplified microwave signal to theimpedance presented by the radial waveguide, a dummy load, and acirculator that shunts power reflected back from the radial waveguidetoward the first electronics set, into the dummy load. The signalgenerator adjusts the phase offset, and the tuner matches the impedance,concurrently with one another.

In an embodiment, a method for controlling a plasma within a processchamber includes generating, with a signal generator, a first microwavesignal and a second microwave signal, the first and second microwavesignals having a common frequency and a phase offset therebetween thatis determined at least in part by the singal generator responding to adigital correction signal. The method also includes amplifying the firstand second microwave signals to provide respective first and secondamplified microwave signals, and transmitting the first and secondamplified microwave signals into a radial waveguide proximate theprocess chamber such that microwaves propagate from the radial waveguideinto the process chamber to provide energy for the plasma. The methodalso includes generating analog signals with at least two monitoringantennas disposed within the radial waveguide, determining the digitalcorrection signal based at least on the analog signals from the at leasttwo monitoring antennas, and transmitting the digital correction signalto the signal generator.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the invention. The features and advantages ofthe invention may be realized and attained by means of theinstrumentalities, combinations, and methods described in thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be understood by reference to the followingdetailed description taken in conjunction with the drawings brieflydescribed below, wherein like reference numerals are used throughout theseveral drawings to refer to similar components. It is noted that, forpurposes of illustrative clarity, certain elements in the drawings maynot be drawn to scale. Specific instances of an item may be referred toby use of a numeral in parentheses (e.g., monitoring antennas 311(1),311(2)) while numerals without parentheses refer to any such item (e.g.,monitoring antennas 311). In instances where multiple instances of anitem are shown, only some of the instances may be labeled, for clarityof illustration.

FIG. 1 schematically illustrates major elements of a single wafer,semiconductor wafer processing system, according to an embodiment.

FIGS. 2A and 2B are schematic cross-sections illustrating selectedstructure of a radial waveguide and a process chamber of the singlewafer, semiconductor wafer processing system of FIG. 1.

FIG. 3 is a schematic diagram of major components of a system forproviding microwaves to a plasma chamber utilizing a radial waveguide,in an embodiment.

FIG. 4 is a schematic diagram of major components of a system thatprovides post-match control of microwaves in a radial waveguide, in anembodiment.

FIG. 5 schematically illustrates a radial waveguide that is powered byfour electronics sets and is monitored by four monitoring antennas, inan embodiment.

FIG. 6 is a schematic diagram illustrating implementations of the signalcontroller and dual phase signal generator shown in FIG. 4, in anembodiment.

FIG. 7 illustrates exemplary operation of a first portion of an IQdemodulator shown in FIG. 6.

FIG. 8 is a schematic diagram of major components of a system thatprovides post-match control of microwaves in a radial waveguide, in anembodiment.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates major elements of a plasma processingsystem 100, according to an embodiment. System 100 is depicted as asingle wafer, semiconductor wafer processing system, but it will beapparent to one skilled in the art that the techniques and principlesherein are applicable to a plasma processing system for any type ofworkpiece (e.g., items that are not necessarily wafers orsemiconductors). Processing system 100 includes a housing 110 for awafer interface 115, a user interface 120, a process chamber 130, acontroller 140 and one or more power supplies 150. Process chamber 130includes one or more wafer pedestals 135, upon which wafer interface 115can place a workpiece 50 (e.g., a wafer, but could be a different typeof workpiece) for processing. A radio frequency generator (RF Gen) 165supplies power to create a plasma within process chamber 130.Specifically, RF Gen 165 powers a radial waveguide 167 that may bedisposed above or below process chamber 130, and is shown in FIG. 2 asabove chamber 130. Process chamber 130 is proximate radial waveguide167, and is bounded adjacent to radial waveguide 167 by a plate 169 thatis formed of a material that is permeable to electromagnetic fields butnot to air or process gases utilized in chamber 130. Thus, plate 169 cansupport a pressure difference between radial waveguide 167 and chamber130, while allowing microwaves within radial waveguide 167 to propagateinto chamber 130. Plate 169 may be formed, for example, of ceramic. Theelements shown as part of system 100 are listed by way of example andare not exhaustive. Many other possible elements, such as: pressureand/or flow controllers; electrodes, magnetic cores and/or otherelectromagnetic apparatus; mechanical, pressure, temperature, chemical,optical and/or electronic sensors; viewing and/or other access ports;and the like may also be included, but are not shown for clarity ofillustration. Internal connections and cooperation of the elements shownwithin system 100 are also not shown for clarity of illustration. Inaddition to RF generator 165, other representative utilities such asgases 155, vacuum pumps 160, and/or general purpose electrical power 170may connect with system 100. Like the elements shown in system 100, theutilities shown as connected with system 100 are intended asillustrative rather than exhaustive; other types of utilities such asheating or cooling fluids, pressurized air, network capabilities, wastedisposal systems and the like may also be connected with system 100, butare not shown for clarity of illustration.

FIGS. 2A and 2B are schematic cross-sections illustrating selectedstructure of radial waveguide 167 and process chamber 130, FIG. 1. FIG.2A is a vertical cross-section of radial waveguide 167, process chamber130 and a workpiece 50 therein. A broken line 2B-2B′ indicates a furthercross-sectional view illustrated in FIG. 2B. Radial waveguide 167 is asubstantially cylindrical and closed shape, except for slots 168 formedin an undersurface thereof that allow microwaves to propagate intoprocess chamber 130, ports for providing and/or measuring microwaves,and other minor penetrations (such ports and penetrations are not shownin FIGS. 2A/2B). Slots 168 may for example form a radial line slotantenna. Process chamber 130 is substantially radially symmetric along acommon axis with radial waveguide 129. Microwaves propagate from radialwaveguide 167 into process chamber 130 through slots 168 and throughplate 169 to provide energy for igniting and/or maintaining plasma 60.Pedestal 135 is configured to present a workpiece 50 to plasma 60 forprocessing. Process chamber 130 may include ports and/or mechanicalopenings (not shown) for insertion and/or withdrawal of workpiece 50,introduction of gases to form plasma 60, removal of plasma and gaseousreaction products, sensors, viewing and the like.

FIG. 3 is a schematic diagram of major components of a system 200 forproviding microwaves to a plasma chamber utilizing a radial waveguide,in an embodiment. A radial waveguide 210 of system 200 may be utilizedfor example as radial waveguide 167, FIG. 1. In general, system 200powers radial waveguide 210 at two locations noted as P and Q in FIG. 3,with locations P and Q being driven roughly π/2 out of phase with oneanother by electronics sets 225(1), 225(2) described below. Radialwaveguide 210 is thus considered a “dual driven” radial waveguide; thedual driven mode of operation provides high microwave energy densityderived from two sets of driving electronics rather than a single setoperating at double the power. Use of two (or more) sets of drivingelectronics, each operating at lower power than a single set at highpower, may be advantageous. An electronics set operating at higher powermay require components having higher voltage, current, or heatdissipation ratings that may be much more expensive or difficult toobtain than components for lower power sets. For example, microwavefield effect transistors (FETs) of low cost and high quality haverecently become available for use in electronics sets 225 herein, buthigh voltage, current, and/or power dissipation versions of such FETsmay remain costly or difficult to obtain.

Operation of system 200 is best understood as starting with a dual phasesignal generator 215 that provides two microwave signals 220(1), 220(2)that are at the same frequency, but are π/2 out of phase with oneanother. Microwave signals 220(1), 220(2) drive circuits that arereferred to as a first set 225(1) and a second set 225(2). Each set225(1), 225(2) begins with a solid state amplifier 230 that boosts thepower of respective microwave signals 220(1), 220(2) to create amplifiedmicrowave signals 235(1), 235(2). Solid state amplifiers 230 may includeone or more microwave FETs, as discussed above. Each amplified microwavesignal 235(1), 235(2) passes into and through a circulator 240 thatserves to protect the respective solid state amplifiers 230 from powerreflections from radial waveguide 210. Circulators 240 thus pass inputpower from solid state amplifiers 230 into respective tuners 250, whileshunting any power that is reflected back into dummy loads 245.

Tuners 250 adjust impedance seen by the amplified microwave signals235(1), 235(2) so as to match an impedance presented by components suchas converters 255, radial waveguide 260 and an adjacent process chamber(e.g., process chamber 130, FIG. 1, not shown in FIG. 3). Tuners 250 maybe, for example, three-pole stub tuners. The amplified, tuned signalsthen pass through respective coaxial-to-waveguide converters 265 andinto radial waveguide 210 at respective waveguides with radiatingapertures 270.

As part of the tuning required to achieve acceptable impedance matching,tuners 250 can change the phase of signals passed toward radialwaveguide 210, such that although the signals are supplied at positionsthat are exactly π/2 out of phase around the circumference of radialwaveguide 210, the signals themselves may no longer be exactly π/2 outof phase. That is, instead of exciting a symmetric, circularpolarization mode in radial waveguide 210, an asymmetric, ellipsoidallypolarized mode may be excited. This asymmetry in the microwaveconfiguration can lead, in turn, to process aberrations in an adjacentprocess chamber. For example, an asymmetric microwave configuration canlead to a correspondingly asymmetric plasma and consequently to localskews in depth of plasma etching.

Embodiments herein recognize that as wafer sizes grow larger and thegeometries produced in semiconductor fabrication grow smaller, the needfor uniformity control of all aspects of the processing environmentaround the wafer increases. Therefore, embodiments herein adjust themicrowave configuration that generates the plasma, not only to matchimpedance, but also to adjust phase and/or amplitude after impedance ismatched, for improved symmetry of the plasma generated around the wafer.Even when careful attention is paid to symmetry of a process chamber,placement of a wafer in the process chamber, and the like, asymmetriesin a plasma can arise from many causes (e.g., mechanically asymmetricports, sensors, wafer placement, wafer flats, cabling length and thelike) such that control of phase and/or amplitude, in addition toimpedance matching, may provide an extra and useful degree of freedomfor improving uniformity in plasma processing.

FIG. 4 is a schematic diagram of major components of a system 300 thatprovides post-match control of microwaves in a radial waveguide, in anembodiment. System 300 may be utilized to excite a plasma in an adjacentplasma chamber. In general, system 300 has many of the same componentsas, and works similarly to, system 200 (FIG. 3). However, system 300independently adjusts amplitude of, and/or a phase offset between,microwave signals 320(1) and 320(2) to control phase at points P and Q,for example to be utilized as a degree of freedom for optimizing processuniformity.

In system 300, a radial waveguide 210 may be utilized for example asradial waveguide 167, FIG. 1. System 300 powers radial waveguide at twolocations noted as P and Q in FIG. 1, with locations P and Q beingdriven roughly π/2 out of phase with one another. Like system 200,operation of system 300 can be understood starting with a dual phasesignal generator 315 that provides microwave signals 320(1), 320(2) thatare at the same frequency. However, dual phase signal generator 315receives a correction signal 313 from a signal controller 312 thatprovides information for adjustment of signals 320(1), 320(2). Forexample, correction signal 313 may direct dual phase signal generator315 to provide a corrected or targeted phase offset between microwavesignals 320(1), 320(2). Thus, in system 300, microwave signals 320(1),320(2) may be out of phase with one another by π/2, or by π/2 plus orminus the target phase difference, such that a measured phase differenceat points P and Q is as intended, as discussed below. In anotherexample, correction signal 313 may direct dual phase signal generator315 to boost and/or attenuate one or both of microwave signals 320(1),320(2).

At this point, it should be noted that signal generator 315 is termed a“dual phase signal generator” herein, but considering that otherembodiments may be driven at more than two points by a signal generatorthat generates more than two signals of identical frequency anddiffering phase (see, e.g., FIG. 8) it is understood that the “dualphase” aspect is for convenient reference. Furthermore, in embodiments,signal generator 315 may control amplitude of signals 320, as well asphase thereof. Thus, dual phase signal generator 315 is simply aspecific case of a “signal generator” as discussed elsewhere herein.

Like system 200, microwave signals 320(1), 320(2) drive respective solidstate amplifiers 230 that boost power to create amplified microwavesignals 335(1), 335(2), which in turn pass into and through circulators240. Circulators 240 pass amplified microwave signals 335(1), 335(2)into respective tuners 250 while shunting any power reflected back intodummy loads 245. Tuners 250 adjust impedance seen by the amplifiedmicrowave signals 335(1), 335(2) so as to match an impedance presentedby components such as converters 255, radial waveguide 260 and anadjacent process chamber (e.g., process chamber 130, FIG. 1, not shownin FIG. 4). The amplified, tuned signals then pass through respectivecoaxial-to-waveguide converters 265 and into radial waveguide 210 atrespective waveguides with radiating apertures 270.

Monitoring antennas 311(1) and 311(2), disposed proximate to points Pand Q respectively, provide analog signals to signal controller 312through their respective connections 318(1) and 318(2), capturing anyphase offset introduced by tuners 250. Monitoring antennas 311 maymonitor either an electrical field or a magnetic field component ofmicrowaves in radial waveguide 210. When electrical fields aremonitored, it is appreciated that metal of radial waveguide 210 mayreduce electrical fields in close proximity thereto, such that careshould be taken to locate monitoring antennas 311 far enough from radialwaveguide 210 to provide sufficient sensitivity. Signal controller 312receives signals from monitoring antennas 311(1) and 311(2) throughtheir respective connections 318(1) and 318(2) and determines amplitudeof, and a phase offset between, signals at points P and Q. For example,signal controller 312 may perform in-phase and quadrature-phasedemodulation (IQ demodulation) to measure amplitude and phase offset ofthe signals from monitoring antennas 311(1) and 311(2) (see also FIG.9). Signal controller 312 then utilizes the measured phase offset and/oramplitudes to calculate and provide a corresponding digital correctionsignal 313 to dual phase signal generator 315. Digital correction signal313 may be chosen to be a desired phase offset (e.g., a value of π/2) oran offset from an assumed, desired phase difference (e.g., a correctionfactor that is zero when the desired phase difference is attained).Alternatively, digital correction signal may be chosen to adjustamplitude of one or both of microwave signals 320(1), 320(2). Dual phasesignal generator 315 then provides microwave signals 320(1) and 320(2)with a phase offset and/or amplitudes such that when the microwavesignals propagate through the system, the phase offset between points Pand Q is driven to the desired phase difference, and/or the amplitudesmeasured at points P and Q are as desired.

Optionally, a target input device 314 may provide one or more targetparameters 316 to signal controller 312. Target input device 314 may beimplemented in a variety of ways, such as by physical switches providingan output that is received directly by signal controller 312, or as apart of system management hardware and software that acquires the targetparameters from a user interface (e.g., a keyboard, other buttons, or agraphical user interface (GUI)). Target parameters 316 may include, forexample, a desired phase difference as measured at monitoring antennas311(1) and 311(2), or amplitude adjustments to either or both ofmicrowaves driven into radial waveguide 210. Target parameters 316 canbe utilized by signal controller 312 along with the analog signals frommonitoring antennas 311(1) and 311(2), to generate digital correctionsignal 313. For example, when a target phase difference is utilized,digital correction signal 313 may be generated first based on thesignals from monitoring antennas 311(1) and 312(1), after which digitalcorrection signal 313 may be adjusted by adding or subtracting targetparameter 316. Once digital correction signal 313 is transmitted, dualphase signal generator 315 provides signals 320(1) and 320(2) with acorresponding offset until the phase offset between points P and Q isdriven according to the target parameter, and digital correction signal313 is driven to its target value, or zero. In another example, when atarget amplitude adjustment is utilized, dual phase signal generator 315can adjust amplitude of either or both of signals 320(1), 320(2) inresponse thereto.

Optional target input device 314 provides a useful, independent degreeof freedom for optimizing a semiconductor processing system thatincludes system 300 or other systems with a similar capability, asdisclosed herein. For example, the corresponding semiconductorprocessing system may be optimized by processing (e.g., etching) wafers,which may have test patterns printed thereon. Each wafer could beprocessed with identical processing parameters except for a differenttarget parameter entered into target input device 314. The performanceof the system could be evaluated by measurements of the wafers that areindicative of performance of the etch system (e.g., etch rate,selectivity, linewidth change due to etch, and the like) as well assystem monitors (e.g., system stabilization times, endpoint detectionparameters, etc.) An optimized value of the target parameter could thenbe selected, based on the wafer measurements, the system monitors and/ora combination thereof.

It will be understood by one skilled in the art that while signalcontroller 312 cooperates with dual phase signal generator 315 to adjustphase of microwave signals 320(1) and 320(2), tuners 250 also continueto adjust impedance matching to minimize reflected power. Thus, system300 does not sacrifice impedance matching, but rather provides theadditional capability of phase and/or amplitude adjustment for the dualdriven radial waveguide, to optimize plasma symmetry in an adjacentprocess chamber. That is, in embodiments, signal generator 315 adjuststhe phase offset, and tuners 250 provide the impedance matching,concurrently with one another during the operation of system 300. Inother embodiments, signal generator 315 adjusts the amplitude, andtuners 250 provide the impedance matching, concurrently with one anotherduring the operation of system 300.

Embodiments that provide post-match control of microwaves in a radialwaveguide are not limited to the cases of two microwave generatingelectronics sets and two antennas that are illustrated in FIG. 4. Forexample, FIG. 5 schematically illustrates a system 500 having a radialwaveguide 510 that is powered by four electronics sets, 525(1) through525(4) and is monitored by four monitoring antennas, 555(1) through555(4). As shown in FIG. 5, electronics sets 525 are disposed at 90degree intervals about a periphery of radial waveguide 510, withmonitoring antennas 555 disposed at midpoints therebetween. While twomonitoring antennas 555 disposed orthogonally to one another aretheoretically sufficient to evaluate whether a microwave distributionwithin radial waveguide 510 is symmetrical, four antennas 555 andcorresponding correction factors for four electronics sets 525 may beutilized to provide further degrees of freedom in process control.Electronics sets 525 are driven by a signal generator that provides fourmicrowave signals of the same frequency but different phases (e.g.,analogous to operation of dual phase signal generator 315) that receivescorrection factors from a quad signal controller (e.g., analogous tosignal controller 312). An optional target input device (analogous totarget input device 314) may provide target parameters applicable to anyof the signals driven by the signal generator and/or the signalsdetected by any of the monitoring antennas 555. The locations ofelectronics sets 525 and monitoring antennas 555 shown in FIG. 5 maysimplify calculation of expected phase of microwaves monitored at themonitoring antennas, and corresponding digital correction factors to beapplied to the microwave signals that are input to the electronics sets,but other arrangements will be apparent to those skilled in the art.Also, similar embodiments may utilize more or fewer electronics sets 525and/or monitoring antennas 555, with appropriate adjustments to input oftarget parameters and/or calculation of signals driven by acorresponding signal generator. A semiconductor processing system thatincludes radial waveguide 510, electronics sets 525 and monitoringantennas 555 may be optimized in a manner analogous to the proceduredescribed above in connection with FIG. 4, except that multiple targetparameters may be implemented and evaluated, alone and/or in combinationwith one another.

FIG. 6 is a schematic diagram illustrating implementations of signalcontroller 312 and dual phase signal generator 315, in an embodiment.The embodiment illustrated in FIG. 6 could support any of the systemsshown in FIG. 4 directly, and the principles now explained can beduplicated or otherwise modified in ways that will be readily apparentto support the system illustrated in FIG. 5.

In the embodiment illustrated in FIG. 6, signal controller 312 includesa control clock (CLK) 602 that generates a 40 MHz waveform and a highfrequency clock (HCLK) 604 that generates a 2.449 GHz waveform. Clock602 serves to provide a gating time signal for successive demodulations.Clock 604 provides a reference frequency for dual phase signal generator315 (e.g., a frequency at which radial waveguide 167, FIGS. 2A and 2B,radial waveguide 210, FIGS. 3-4 or radial waveguide 510, FIG. 5, isdriven to support a plasma powered thereby) and can therefore providethe same reference frequency for IQ demodulation purposes. Given theseunderstandings of how clocks 602 and 604 are utilized, the exactfrequencies of clocks 602 and 604 are not critical and may be differentin other embodiments. In particular, a higher speed of clock 602 willforce more frequent repetition of the calculations discussed below,leading to faster plasma adjustment and settling times for an entiresystem, but will increase system power requirements and may lead to aneed for higher performance versions of components 606 and 608 discussedbelow. A lower speed of clock 602 may increase plasma adjustment andsettling time achievable by the system but may reduce system powerrequirements and may allow use of lower performance versions ofcomponents 606 and 608.

Signal controller 312 also includes an IQ demodulator 606 and amicrocontroller 608 executing software 609. At intervals established byclock 602, an IQ demodulator 606 performs IQ demodulation of each of thesignals provided through connections 318(1) and 318(2), and generatestherefrom a digital in-phase signal Xni and a digital quadrature-phasesignal Xnq, where n is 1 or 2 corresponding to connections 318(1) and318(2) respectively. Digital in-phase and quadrature-phase signals Xniand Xnq characterize the corresponding received signal in that Xni isthe real part of signal n, and Xnq is the imaginary part of signal n. Aphase φn of signal n is given by φn=tan (Xni/Xnq) and an amplitude An ofsignal n is given by An=√{square root over (Xni²+Xnq²)}. The IQdemodulation of each of the signals proceeds in parallel such that foreach interval, IQ demodulator 606 provides corresponding digital signalsX1 i, X1 q, X2 i, X2 q, as shown.

FIG. 7 illustrates exemplary operation of a first portion 606(a) of IQdemodulator 606 that processes a signal received from connection 318(1)to yield X1 i and X1 q; it is understood that IQ demodulator 606 alsohas a second portion that performs similar processing with respect to asignal received from connection 318(2) to yield X2 i and X2 q. Anoptional bandpass filter 620 may be utilized to clean up the signal fromconnection 318, especially to eliminate harmonics of the main receivedfrequency, which in this example is around 2.450 GHz. An exemplarypassband of filter 620 might be, for example, 2.45 GHz±0.05 GHz; inembodiments, the width of the passband could be considerably higher, upto perhaps 20% of the received frequency and not necessarily centeredabout the received frequency. Demodulation proceeds by mixing the signalfrom connection 318(1) with the signal from clock 604 to generate anintermediate frequency (IF) signal. It should be understood from thediscussion above and further below that the clock 604 frequency will berelated to the frequency produced by signal generator 315 and propagatedinto radial waveguide 210 to produce a usable IF signal. In the presentexample clock 604 operates at 2.449 GHz while dual phase signalgenerator 315 produces a 2.450 GHz signal, thus yielding a 1 MHz IFsignal. FIG. 7 labels parts of portion 606(a) of demodulator 606 as “HF”(high frequency), “IF” and “DIGITAL” for easy understanding of thesignals being processed in each part.

In certain embodiments, in the IF part of portion 606(a) a bandpass orlowpass filter 624 cleans up the signal from mixer 622. An exemplarypassband of filter 620 might be, for example, 0 Hz (if lowpass) or 0.5MHz (if bandpass) to around 2 MHz. An analog to digital converter 626converts the IF signal to a digital sample on intervals determined fromclock 602; further processing takes place in the digital part of portion606(a).

Copies 628(a). 628(b) of the digital sample are mixed with valuescorresponding to cos(ωn) and −sin(ωn), where ω is defined as2πf_(IF)/f_(s), where f_(s) is a sampling frequency of clock 602 (40 MHzin this example), f_(IF) is the microwave signal frequency projected tothe IF band (1 MHz in this example). The cos(ωn) and −sin(ωn) values aregenerated from a read-only-memory (ROM) 630 at the clock 602 samplingfrequency, and are multiplied with copies 628(a), 628(b) at digitalmixers 632(a), 632(b) to form the resulting digital outputs X1 i and X1q.

In certain embodiments, digital low pass filters 634(a) and 634(b) canbe utilized to eliminate high frequency digital noise from X1 i and X1q. Typical cutoff values of digital low pass filters 634(a) and 634(b)are for example 1 kHz.

Returning to FIG. 6, from IQ demodulator 606, digital outputs X1 i, X1q, X2 i and X2 q pass to microcontroller 608, that generates correctionsignal 313 therefrom. Microcontroller 608 executes software 609 (whichmay be stored in nontransitory, computer-readable media that forms partof microcontroller 608, or may be external to microcontroller 608) togenerate correction signal 313. Software 609 is implemented to generatecorrection signal 313 in cooperation with operation of dual phase signalgenerator 315. For example, if default operation of dual phase signalgenerator 315 is to generate signals 320(1) and 320(2) with a phaseoffset of π/2, the default value of correction signal 313 may be zero;alternatively, dual phase signal generator 315 may expect correctionsignal 313 to completely specify a phase offset between signals 320(1)and 320(2), in which case the default value of correction signal 313 maybe π/2. Also, when optional target input device 314 is implemented,microcontroller 608 receives target parameter 316 therefrom, andsoftware 609 implements adjustments to correction signal 313 based ontarget parameter 316.

Dual phase signal generator 315 receives correction signal 313 fromsignal controller 312 (specifically, from microcontroller 608) andprovides signals 320(1) and 320(2) with a phase offset indicated bycorrection signal 313, at two outputs Vout1 and Vout2. Dual phase signalgenerator 315 may include, for example, a direct digital synthesizerthat generates two analog outputs, each at the nominal IF frequencydiscussed in connection with IQ demodulator 606, that are subsequentlymixed with the signal from clock 604 to form the frequencies of signals320. For example, in consistency with the examples above, the directdigital synthesizer would create analog outputs at 1 MHz frequency that,when mixed with the 2.449 GHz frequency of clock 604, would providesignals 320 at 2.450 GHz. Signals 320 then transmit to their respectiveelectronics sets, as shown in FIG. 4, radiated into respective radialwaveguides 210 and received back into connections 318(1), 318(2).

In embodiments, clock 604 may not be part of signal controller 312, butmay instead be part of a signal generator (e.g., dual phase signalgenerator 315) which may originate the clock 604 signal and provide anoutput thereof to IQ demodulator 606 for use as a reference clock.Similarly, clock 602 may also be generated by a signal controller orsome other part of a system that includes signal controller 312.

FIG. 8 is a schematic diagram of major components of a system 700 thatprovides post-match control of microwaves in a radial waveguide, in anembodiment. System 700 may be utilized, for example to excite a plasmain an adjacent plasma chamber. In general, system 700 has many of thesame components as, and works similarly to, systems 200 and 300, (FIGS.3-4). However, system 700 does not include monitoring antennas or acorresponding signal controller providing feedback to signal generator315. Instead, a target input device 714 provides an ability to provideone or more target parameters such as phase offset, amplitudeadjustments, or both to signal generator 315 and/or to solid stateamplifiers 230. When target input device 714 specifies a phase offset asthe target parameter, the phase offset is provided by signal generator315 in the form of a corresponding phase offset between signals 320(1)and 320(2). When input device specifies amplitude as the targetparameter, the corresponding effect may be provided by signal generator315 (e.g., in the form of amplitude(s) of signals 320(1) and/or 320(2))or by one or both of solid state amplifiers 230 (e.g., in the form ofadjusting gain of one or both of solid state amplifiers 230, so that theresulting amplitude is provided to radial waveguide 210). Whether phaseor amplitude is selected as the target parameter, target input device714 allows an operator of system 700 to optimize the selected targetparameter independently of actions of tuners 250, which continue tomatch impedance.

It should be understood that an ability to set and/or adjust gain ofsolid state amplifiers 230 as shown in FIG. 8 may also be utilized inembodiments wherein antennas provide feedback and a signal controlleradjusts phase and/or amplitude based on the feedback, (e.g., systems 300and 500 (FIGS. 4, 5)).

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Additionally, a number of well-known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent invention. Accordingly, the above description should not betaken as limiting the scope of the invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the electrode” includesreference to one or more electrodes and equivalents thereof known tothose skilled in the art, and so forth. Also, the words “comprise,”“comprising,” “include,” “including,” and “includes” when used in thisspecification and in the following claims are intended to specify thepresence of stated features, integers, components, or steps, but they donot preclude the presence or addition of one or more other features,integers, components, steps, acts, or groups.

What is claimed is:
 1. A system that provides post-match control ofmicrowaves in a radial waveguide, comprising: the radial waveguide; asignal generator that provides a first microwave signal and a secondmicrowave signal, the first and second microwave signals having a commonfrequency, wherein the signal generator adjusts a phase offset betweenthe first and second microwave signals in response to a digitalcorrection signal; a first electronics set and a second electronics set,wherein each of the first and second electronics sets: amplifies arespective one of the first and second microwave signals to providerespective first and second amplified microwave signals, transmits therespective one of the first and second amplified microwave signals intothe radial waveguide, and matches an impedance of the respective one ofthe first and second amplified microwave signals to an impedancepresented by the radial waveguide; at least two monitoring antennasdisposed within the radial waveguide; and a signal controller that:receives analog signals from the at least two monitoring antennas;determines the digital correction signal based at least on the analogsignals from the at least two monitoring antennas; and transmits thedigital correction signal to the signal generator.
 2. The system thatprovides post-match control of microwaves in a radial waveguide asrecited in claim 1, further comprising: a target input device configuredto provide a target parameter to the signal controller; and wherein: thesignal controller determines the digital correction signal based on theanalog signals from the at least two monitoring antennas and the targetparameter.
 3. The system that provides post-match control of microwavesin a radial waveguide as recited in claim 1, wherein the firstelectronics set includes a tuner that matches an impedance of the firstamplified microwave signal to an impedance presented by the radialwaveguide; wherein the signal generator adjusts the phase offset, andthe tuner matches the impedance, concurrently with one another.
 4. Thesystem that provides post-match control of microwaves in a radialwaveguide as recited in claim 1, wherein the first electronics setincludes: a dummy load; and a circulator that shunts power reflectedback from the radial waveguide toward the first electronics set, intothe dummy load.
 5. The system that provides post-match control ofmicrowaves in a radial waveguide as recited in claim 1, wherein thefirst electronics set includes a solid state amplifier having amicrowave field effect transistor that amplifies the first microwavesignal to provide the first amplified microwave signal.
 6. The systemthat provides post-match control of microwaves in a radial waveguide asrecited in claim 1, wherein the monitoring antennas are disposedproximate to locations at which the first and second electronics setstransmit the respective first and second amplified microwave signalsinto the radial waveguide.
 7. A system for plasma processing of aworkpiece, comprising: a process chamber configured to create a plasmafor the plasma processing; a radial waveguide, adjacent to the processchamber, configured to generate microwaves for transmission to theprocess chamber to supply energy for the plasma; a signal generator thatprovides a first microwave signal and a second microwave signal, thefirst and second microwave signals having a common frequency, whereinthe signal generator adjusts a phase offset between the first and secondmicrowave signals in response to a digital correction signal; a firstelectronics set and a second electronics set, wherein each of the firstand second electronics sets: amplifies a respective one of the first andsecond microwave signals to provide an amplified microwave signal,transmits the respective one of the first and second amplified microwavesignals into the radial waveguide to produce microwaves therein; andmatches an impedance of the respective one of the first and secondamplified microwave signals to an impedance presented by the radialwaveguide; at least two monitoring antennas disposed within the radialwaveguide that produce analog signals in response to the microwaves; anda signal controller that: receives the analog signals from the at leasttwo monitoring antennas, determines the digital correction signal basedat least on the analog signals, and transmits the digital correctionsignal to the signal generator; and wherein the first electronics setincludes: a tuner that matches the impedance of the first amplifiedmicrowave signal to the impedance presented by the radial waveguide, adummy load, and a circulator that shunts power reflected back from theradial waveguide toward the first electronics set, into the dummy load;and the signal generator adjusts the phase offset, and the tuner matchesthe impedance, concurrently with one another.
 8. The system for plasmaprocessing of a workpiece as recited in claim 7, wherein the radialwaveguide comprises a radial line slot antenna for transmitting themicrowaves into the process chamber.
 9. The system for plasma processingof a workpiece as recited in claim 8, further including a ceramic platethat bounds the process chamber adjacent to the radial line slot antennaof the radial waveguide, the ceramic plate supporting a pressuredifference between the radial waveguide and the process chamber, whileallowing the microwaves to propagate from the radial waveguide into theprocess chamber.
 10. A method for controlling a plasma within a processchamber, comprising: generating, with a signal generator, a firstmicrowave signal and a second microwave signal, the first and secondmicrowave signals having a common frequency, and a phase offsettherebetween that is determined at least in part by the signal generatorresponding to a digital correction signal; amplifying the first andsecond microwave signals to provide respective first and secondamplified microwave signals; transmitting the first and second amplifiedmicrowave signals into a radial waveguide proximate the process chamber,such that microwaves propagate from the radial waveguide into theprocess chamber to provide energy for the plasma; generating analogsignals from the microwaves with at least two monitoring antennasdisposed within the radial waveguide; determining the digital correctionsignal based at least on the analog signals from the at least twomonitoring antennas; and transmitting the digital correction signal tothe signal generator.
 11. The method for controlling a plasma within aprocess chamber as recited in claim 10, wherein determining the digitalcorrection signal comprises performing in-phase and quadrature-phasedemodulation on each of the analog signals.
 12. The method forcontrolling a plasma within a process chamber as recited in claim 11,wherein performing in-phase and quadrature-phase demodulation comprises:mixing a reference high frequency signal with one of the the analogsignals to generate an intermediate frequency, and generating digitalin-phase and quadrature-phase signals from the intermediate frequency.13. The method for controlling a plasma within a process chamber asrecited in claim 12, further comprising: utilizing a microprocessor togenerate the digital correction signal based on the digital in-phase andquadrature-phase signals; and wherein generating the first microwavesignal comprises: generating an analog output at the intermediatefrequency, utilizing the digital correction signal, and mixing theanalog output with the reference high frequency signal to form the firstmicrowave signal.
 14. The method for controlling a plasma within aprocess chamber as recited in claim 10, further comprising: receiving atarget parameter from a target input device; and wherein determining thedigital correction signal further comprises adjusting the digitalcorrection signal according to the target parameter.
 15. The method forcontrolling a plasma within a process chamber as recited in claim 14,wherein the target parameter is a phase difference, and adjusting thedigital correction signal comprises adjusting the phase offset accordingto the phase difference.